hoppers) is a direct cause of repair, replacement and downtime and represents a major factor in the cost of production. Abrasive wear is also an important factor in determining the life of tillage and construction equipment and in the case of tillage tools has a direct impact on the draft forces required to pull the plough. There is therefore considerable interest in the design, development and use of cost effective wear resistant materials for such applications.
The wear resistance of a material cannot be predicted reliably from simple properties such as bulk hardness, elastic modulus or tensile strength. There is therefore a need for a reliable and convenient approach to the study of abrasive wear properties.
A number of standard methods have been developed with the aim of producing test data that will reproducibly rank materials under a specified set of conditions. The most widely used are the sand/rubber wheel test in dry (ASTM G65) and wet (ASTM G105) conditions and a sand/steel wheel test in wet conditions (ASTM B611). These define tests under dry or slurry conditions with specified loads, wheel speeds and sand feed rate. In all cases the abrasive used is rounded quartz grain sand.
The TE 65 Multiplex Sand/Wheel Abrasion Tester is a development of a machine designed by Dr M. Gee of the Centre for Materials Measurement and Technology, National Physical Laboratory (NPL), UK. The TE 65 is designed to perform tests according to the conditions described in the following methods:
- ASTM G65 Standard Test Method for Measuring Abrasion Using the Dry Sand/Rubber Wheel Apparatus
- ASTM G105 Standard Test Method for Conducting Wet Sand/Rubber Wheel Abrasion Tests
- ASTM B611 Test Method for Abrasive Wear Resistance of Cemented Carbides
The machine is floor standing with test assemblies mounted on a back-plate and abradant discharged downwards into a hopper. Load is applied by pneumatic bellows in conjunction with a manually adjusted precision regulator, with a force transducer for load measurement. Speed set-point control is manual, implemented via a PLC, with input via touch-screen.
Standard Test Configurations
ASTM G65 uses hopper fed sand through a defined nozzle and loads the test piece sideways on to the wheel.
The other standards have a fluid trough and the slurry is agitated by the wheel rotation. ASTM B611 uses a steel wheel, thus providing higher stress abrasion than the rubber wheel tests.
TE 65/PA Precision Abradant Feed System
The TE 65 includes the option of a second loading system that presses the specimen on to the top of the wheel, with the specimen horizontal.
In practice, abrasive materials will vary considerably in hardness, crushing strength and shape from the sand specified in the ASTM standards. Rankings of wear resistance obtained with quartz sand may bear little relation to wear with other abradants such as sub-angular quartz, silica sand, alumina, sinter, coke and coal. The absolute wear rate and relative ranking of materials are greatly influenced by the following parameters:
- 1. Particle loading, the nominal load carried by each particle of abradant
- 2. Particle size
- 3. Particle speed or cutting speed
- 4. Moisture level
- 5. Abradant properties, namely hardness and crushing strength
- 6. Abradant particle shape or angularity
It is clear, therefore, that a single set of test conditions will not be sufficient for determining the wear resistance of diverse materials. One of the main features of the machine described in the ASTM G65 method is the nozzle: this is critical to determining the mass flow rate of sand and the number of particles in the contact. However it is restricted to one type of sand and there are no facilities for adjusting the mass flow rate. The consumption of sand is also high due to the large mass flow required. Lower flow rates are desirable if non-standard abradants are to be used, thus requiring smaller batches to be produced.
The particle loading is a crucial parameter for a given abradant, as this controls whether the particle cuts or is crushed in the contact. Particle loading needs to be controlled over a wide range of conditions, by adjusting the mass flow and the normal load on the test block.
Wet rubber and steel wheel tests use a large volume of slurry, containing 1.5 kg of sand, that is agitated by paddles on the wheel as it rotates. Smaller quantities may be desirable, if non-standard abradants are to be used.
The TE 65/PA Precision Abradant Feed System is designed to give a range of constant feed rates and produce an even monolayer of particles on the wheel, in front of the contact. The abradant is fed from a hopper to a rotating drum with a shallow groove on its surface. The feed rate is varied by adjusting the speed of the slotted drum. The out-fall from the drum is then guided to the wheel surface down a simple chute and this produces the monolayer on the wheel surface.
Any abradant that does not pass through the contact may be collected separately and therefore the quantity of abradant actually passing the test block may be determined. This is not possible in the ASTM configuration. By having control of the drum speed, much lower abradant mass flow rates can be achieved, than in the ASTM G65 method.
TE 65/FT Force Transducer/Flexure Assembly
The TE 65/FT specimen arm incorporates a strain gauge transducer to measure the dynamic friction. Data is recorded at 1 Hz sampling rate, stored by the PLC and exported on USB stick, for post-processing.
Test Types: ASTM G65, ASTM G105, ASTM B611 Wheel Speed: 10 to 350 rpm Wheel Types: 6.65″ steel wheel as per ASTM B611 9″ rubber wheel as per ASTM G65 Load: 20 to 350 N Specimen Size: 25 mm x 58 mm Specimen Thickness: 6 mm to 16 mm User Interface: PLC with touch-screen Data Acquisition Rate: 1 Hz Data Export: USB stick Motor Type: ac motor with frequency inverter drive TE 65/PA Precision Abradant Feed System Wheel Types: 6.65″ steel wheel as per ASTM B611 9″ rubber wheel as per ASTM G65 Specimen Size: 25 mm x 50 mm Specimen Thickness: 6 mm to 16 mm (10 mm typical) Typical Feed Rate: 60 to 200 g/min (for 600 µm silica sand) TE 65/FT Force Transducer/Flexure Assembly Friction Range: 10 to 200 N Services Electricity: 220/240V, single phase, 50 Hz, 1 kW 110/120 V, single phase, 60 Hz, 1 kW Clean, dry air: 4 cfm at 8 bar (120 psi)
abrasion resistance abrasive wear brittle materials dry sand/rubber wheel dry sand/steel wheel hardmetals materials handling metal matrix composites mining applications slurry abrasion three body abrasion wear by hard particles wet sand abrasion
Paper # 265 Critically Evaluated Abrasion Wear Tests on WC/Co Hardmetals. Gee M G, Roebuck B, Byrne W P, World Tribology Conference, London, September 1997. Paper # 269 Mechanisms of Wear in the High Stress Abrasion of WC/Co Hardmetals. Gee M G, Fang Liang, Roebuck B, Proceedings of PM 99, Turin. Paper # 271 Tungsten Carbide for Abrasion Resistant Applications, Using Powder Metallurgy in Design. Gee M G, Roebuck B, Wear, Corrosion and Fatigue Resistance, Professional Engineering Publishers, April 2000, p 41-59. Paper # 274 Wear of Tungsten Carbide-Cobalt Hardmetals and Hot Isostatically Pressed High Speed Steels under dry Abrasive Conditions. Gant A, Gee M G, Wear 251 (2001) 908-915. Paper # 289 Development of the Dry Sand/Rubber Wheel Abrasion Test. Stevenson A. N. J., Hutchings I. M., Wear 195 (1996) 232-240, Paper # 291 Abrasive Wear Resistance of Plasma-sprayed Tungsten Carbide-cobalt Coatings. Chen H., Hutchings I. M., Surface and Coatings Technology 107 (1998) 106-114, Paper # 295 Abrasive Wear Behaviour of an Alumina-aluminium Co-continuous Composite. Imbeni V Hutchings I. M., Breslin M. C., Wear 233-235 (1999) 462-467, Paper # 313 An NPL Rotating Wheel Abrasion Test. Gee M G, Gant A J, Byrne W P, NPL Measurement Note CMMT(MN)30, November 1998. Paper # 314 Characterisation of Baseline Hardmetals Using Property Maps. Roebuck B, Bennett E G, Byrne W P, Gee M G, NPL Report CMMT(A)172, April 1999. Paper # 315 Abrasion and Reciprocating Wear Testing of Ceramics and Hardmetals. Gee M G, Gant A, Byrne W P, Roebuck B, NPL Report CMMT(A)166, May 1999. Paper # 318 Rotating Wheel Abrasion Tests on Hardmetals and Ceramics. Gee M G, Gant A, NPL Measurement Note CMMT(MN)46, May 1999. Paper # 322 Procedure for Rotating Wheel Abrasion Testing. Gee M G, Gant A, NPL Report MATC(A)54, July 2001.
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